Any vehicle in active service transporting United States mail may display two simultaneously flashing lights to be used for the purpose of warning other vehicle operators of its presence and to exercise caution in approaching, overtaking, or in passing. Such lights may be flashed continuously or actuated by application of the service brake (foot) while the vehicle is either in motion or parked. Such lamps shall have the following specifications and shall meet the following requirements:
(1) Lamps shall be not less than four inches in diameter and shall be powered by a bulb of not less than 21 candlepower with a reflectorization sufficient to assure visibility for at least 500 feet in front and to the rear of the vehicle under normal atmospheric conditions.
(2) Lamps shall be of double face or two way type.
(3) Lamps shall have amber lens to the front and red lens to the rear.
(4) Lamps shall be mounted on the highest part of the top of the vehicle in such a position that illumination from the lights is visible both to the front and rear for the required distance. Lamps shall be spaced laterally as far apart as body construction will permit but not closer than 30 inches. Between the lamps there shall be mounted a 22-inch by seven-inch sign with the wording "U.S. MAIL" in minimum of four-inch letters and of not less than three quarters of an inch in width of strobe, in black on a white background.
(5) This sign and lamps shall be so installed that the sign can be easily lowered and the lamps turned off when the vehicle is not actually engaged in the United States mail service.
(6) Any vehicle in active service transporting United States mail may, as an option to the foregoing, display a flashing red light not less than four inches in diameter with the letters "STOP" printed thereon and a uniform sign not less than 14 inches in diameter approved by the Department of Public Safety with the words printed thereon "U.S. MAIL, WATCH FOR STOPS," which sign and light is to be attached to the rear of such vehicle.
(7) In addition to the above lighting equipment the Department of Public Safety is hereby granted the authority to prescribe rules and regulations for the use of amber colored strobe lights or any other lighting device on mail delivery vehicles. In prescribing the rules and regulations the Department of Public Safety shall seek the advice of the U.S. Postal Service.